/Engine/Source/Runtime/Core/Public/Containers/UnrealString.h
Searches the string for a substring, and returns index into this string of the first found instance. Can search from beginning or end, and ignore case or not. If substring is empty, returns clamped StartPosition.
int32 Find ( const TCHAR * SubStr, [ESearchCase::Type](API\Runtime\Core\Misc\ESearchCase__Type) SearchCase, [ESearchDir::Type](API\Runtime\Core\Misc\ESearchDir__Type) SearchDir, int32 StartPosition ) const